Apparatus and method for shunting induced currents in an electrical lead

ABSTRACT

An electrical lead includes an elongate body having a proximal end portion and a distal end portion, a first electrode disposed adjacent and joined to the distal end portion of the elongate body, and a first conductor extending between the proximal end portion and the distal end portion of the elongate body and being electrically coupled to the first electrode. The medical electrical lead further comprises a second electrode disposed adjacent the first electrode and joined to the elongate body and a capacitive device electrically coupled to the first conductor and the second electrode.

FIELD OF THE INVENTION

[0001] This invention relates to a method and apparatus for providingelectrical stimuli to tissue or receiving electrical stimulicorresponding to one or more conditions in tissue.

DESCRIPTION OF THE RELATED ART

[0002] Since the introduction of the first implantable pacemakers in the1960s, there have been considerable advancements in both the fields ofelectronics and medicine, such that there is presently a wide assortmentof commercially available body-implantable electronic medical devices.The class of implantable medical devices now includes therapeutic anddiagnostic devices, such as pacemakers, cardioverters, defibrillators,neural stimulators, and drug administering devices, among others.Today's state-of-the-art implantable medical devices are vastly moresophisticated and complex than their early counterparts, and are capableof performing significantly more complex tasks. The therapeutic benefitsof such devices have been well proven.

[0003] Modern electrical therapeutic and diagnostic devices for theheart require a reliable electrical connection between the device and aregion of the heart. Typically, an electrical contact, commonly referredto as a “lead,” is used for the desired electrical connection. One typeof commonly used implantable lead is a transvenous lead. Transvenousleads are generally positioned through the venous system to attachand/or electrically connect at their distal end via a tip electrode tothe heart. At their proximal end, they are typically connected to theelectrical therapeutic and/or diagnostic device, which may be implanted.Such leads normally take the form of a long, flexible, insulatedconductor. Among the many advantages of transvenous leads is that theypermit an electrical contact with the heart without physically exposingthe heart itself, i.e., major thoracic surgery is not required.

[0004] Other advancements in medical technology have led to improvedimaging technologies, for example magnetic resonance imaging (MRI). MRIgenerates cross-sectional images of a human body by using nuclearmagnetic resonance (NMR). The MRI process begins with positioning thebody to be imaged in a strong, uniform magnetic field, which polarizesthe nuclear magnetic moments of protons within hydrogen molecules in thebody by forcing their spins into one of two possible orientations. Thenan appropriately polarized radio-frequency field, applied at resonantfrequency, forces spin transitions between these orientations. The spintransitions create a signal, an NMR phenomenon, which can be detected bya receiving coil.

[0005] Further, shortwave diathermy, microwave diathermy, ultrasounddiathermy, and the like have been shown to provide therapeutic benefitsto patients, such as to relieve pain, stiffness, and muscle spasms; toreduce joint contractures; to reduce swelling and pain after surgery; topromote wound healing; and the like. Generally, energy (e.g., shortwaveenergy, microwave energy, ultrasound energy, or the like) is directedinto a localized area of the patient's body.

[0006] Traditionally, however, use of these technologies have beendiscouraged for patients having such implanted medical devices, as theenvironment produced by the MRI or diathermy apparatuses is generallyconsidered hostile to such implantable medical devices. The energyfields, generated during the MRI or diathermy processes, may induce anelectrical current in leads of implantable medical devices. Inconventional leads, the electrical current is typically dissipated viathe lead's tip electrode into tissue adjacent the distal end of thelead. The dissipation of this electrical current may cause resistiveheating in the tissue adjacent the electrode and may result in damage tothe tissue in some cases.

[0007] The present invention is directed to overcoming, or at leastreducing, the effects of one or more of the problems set forth above.

SUMMARY OF THE INVENTION

[0008] In one aspect of the present invention, an electrical lead ispresented. The medical electrical lead includes an elongate body havinga proximal end portion and a distal end portion, a first electrodedisposed adjacent and joined to the distal end portion of the elongatebody, and a first conductor extending between the proximal end portionand the distal end portion of the elongate body and being electricallycoupled to the first electrode. The medical electrical lead furthercomprises a second electrode disposed adjacent the first electrode andjoined to the elongate body and a capacitive device electrically coupledto the first conductor and the second electrode.

[0009] In another aspect of the present invention, a shunting assemblyis presented. The shunting assembly includes an electrode, a conductor,and a capacitive device electrically coupled with the electrode and theconductor.

[0010] In a yet another aspect of the present invention, a device ispresented. The medical device includes a control unit, an elongate bodyhaving a proximal end portion coupled with the control unit and a distalend portion, and a first electrode disposed adjacent and joined to thedistal end portion of the elongate body. The medical device furtherincludes a first conductor extending between the proximal end portionand the distal end portion of the elongate body and being electricallycoupled to the first electrode and the control unit, a second electrodedisposed adjacent the first electrode and joined to the elongate body,and a capacitive device electrically coupled to the first conductor andthe second electrode.

[0011] In another aspect of the present invention, a method is presentedincluding selectively routing an electrical current traveling through aconductor electrically coupled with body tissue over at least one of aprimary path and a secondary path to the body tissue based upon acharacteristic of the electrical current.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear, and in which:

[0013]FIG. 1 is a stylized view of an embodiment of an implantablemedical device according to one embodiment of the present invention,which has been implanted in a human body;

[0014]FIG. 2 is a stylized perspective view of an implantable medicaldevice lead incorporating a shunting assembly according to a first orsecond embodiment of the present invention;

[0015]FIG. 3 is a schematic diagram of the first embodiment of theshunting assembly according to the present invention;

[0016]FIG. 4 is a schematic diagram of the second embodiment of theshunting assembly according to the present invention;

[0017]FIG. 5 is a stylized perspective view of an implantable medicaldevice lead incorporating a shunting assembly according to a thirdembodiment of the present invention;

[0018]FIG. 6 is a schematic diagram of the third embodiment of theshunting assembly according to the present invention;

[0019]FIG. 7 is a partial cross-sectional view of an embodiment of theshunting assembly according to the present invention; and

[0020]FIG. 8 is a block diagram of a method according to the presentinvention.

[0021] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0022] Illustrative embodiments of the invention are described below. Inthe interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

[0023] Embodiments of the present invention concern body-implantablemedical devices having one or more leads that may be used to stimulate atissue of a body and/or sense one or more conditions in the tissue.Examples of such implantable medical devices are implantable coronarypacing devices, pulse generators, defibrillators, neural stimulationdevices, electrogram devices, and the like. Generally, these devicesoperate by monitoring one or more conditions in the tissue and/or bydelivering electrical stimuli to the tissue via the lead or leads. Forexample, such devices may be used to sense cardiac activity, to deliverelectrical pacing stimuli to a portion or portions of a heart, todeliver electrical defibrillating stimuli to a portion or portions ofthe heart, to deliver electrical stimuli to a nerve, to deliverelectrical stimuli to a portion or portions of a nerve bundle, or todeliver electrical stimuli to a portion or portions of a brain. Whilethe description provided herein is directed to an implantable medicaldevice used in a coronary setting, the present invention encompasses anyimplantable medical device, such as those described above, used in anysetting.

[0024]FIG. 1 illustrates an embodiment of an implantable medical device102 according to the present invention that has been implanted in apatient 104. The implantable medical device 102 includes an implantableelectronic device 106 (e.g., a control unit or the like) housed within ahermetically-sealed, biologically-inert canister 108. The canister 108may itself be conductive so as to serve as an electrode in a circuit ofthe implantable medical device 102. One or more leads 110, 112 areelectrically coupled to the implantable electronic device 106 and extendvia a vein 114 of the patient 104 to a tissue, e.g., a portion of aventricle 116, a portion of an atrium 118, a nerve (not shown), a nervebundle (not shown), or the like. The implantable medical device 102 maybe programmed by using a programming unit 120, which may sendinstructions to and receive information from the implantable medicaldevice 102 via radio-frequency signals.

[0025] As shown in FIG. 2, one or more exposed, electrically-conductiveelectrodes, such as a tip electrode 202 or the like, are disposedgenerally near a distal end portion 204 of a body 205 of the lead 110,as well as a distal end of the lead 112 (not shown), if present. Asindicated above, the tip electrode 202 may be used to sense electricalsignals in a tissue, such as in the ventricle 116, in the atrium 118, ina nerve (not shown), in a nerve bundle (not shown), or the like.Further, the tip electrode 202 may be used to deliver electrical stimulito the tissue, such as to deliver electrical stimuli to a portion, orportions, of a heart, to a nerve, or to a portion, or portions, of anerve bundle. The lead 110 further includes a conductor set 206,electrically coupling the implantable electronic device 106, or anelectrical extension (not shown) extending from the implantableelectronic device 106, and one or more electrodes (e.g., the tipelectrode 202 or the like) of the lead 110. Thus, the conductor set 206extends from a proximal end portion (i.e., a portion joinable with theimplantable electronic device 106 or the like) to the distal end portion204 of the body 205.

[0026] In a first embodiment, the implantable medical device 102 is aunipolar device in which the tip electrode 202 may serve as a cathodeand the canister 108 may serve as an anode for pacing, stimulation, orsensing circuitry (not shown) of the implantable medical device 102. Inthis embodiment, as illustrated in FIGS. 2 and 3, a shunting assembly208 includes a ring electrode 302, which is the portion of the shuntingassembly 208 visible in FIG. 2. The conductor set 206 includes a tipconductor 304 that extends through the shunting assembly 208 to the tipelectrode 202. The tip conductor 304 may be a continuous conductor ormay be a plurality of conductors that are electrically interconnected. Acapacitor 306 is electrically coupled between the tip conductor 304 andthe ring electrode 302. The capacitor 306 may take the form of a singlecapacitive device, a plurality of capacitive devices that areelectrically interconnected, or one or more capacitive deviceselectrically interconnected with other electronic devices.

[0027] In a second embodiment, as illustrated in FIGS. 2 and 4, theimplantable medical device 102 is a bipolar device in which the tipelectrode 202 may serve as a cathode for the pacing, stimulation, orsensing circuitry (not shown) of the implantable medical device 102. Inthis embodiment, the shunting assembly 208 includes a ring electrode402, which is the portion of the shunting assembly 208 visible in FIG.2. Further, the ring electrode 402 may serve as an anode for the pacing,stimulation, or sensing circuitry of the implantable medical device 102.The conductor set 206 includes a tip conductor 404 that extends throughthe shunting assembly 208 to the tip electrode 202. The tip conductor404 may be a continuous conductor or may be a plurality of conductorsthat are electrically interconnected. The conductor set 206 furtherincludes a ring conductor 406 extending into the shunting assembly 208and to the ring electrode 402. As in the tip conductor 404, the ringconductor 406 may be a continuous conductor or may be a plurality ofconductors that are electrically interconnected. A capacitor 408 iselectrically coupled between the tip conductor 404 and the ringelectrode 302. The capacitor 408 may take the form of a singlecapacitive device, a plurality of capacitive devices that areelectrically interconnected, or one or more capacitive deviceselectrically interconnected with one or more other electronic devices.

[0028] In a third embodiment, as illustrated in FIGS. 5 and 6, animplantable medical device 102 is a bipolar device in which the tipelectrode 502 may serve as a cathode and a first ring electrode 503 mayserve as an anode for the pacing, stimulation, or sensing circuitry (notshown) of the implantable medical device 102. In this embodiment, ashunting assembly 504 includes a second ring electrode 604, which is theportion of the shunting assembly 504 visible in FIG. 5. A conductor set506 includes a tip conductor 606 that extends through the first ringelectrode 503 and the second ring electrode 604 to the tip electrode502. The tip conductor 606 may be a continuous conductor or may be aplurality of conductors that are electrically interconnected. Theconductor set 506 further includes a ring conductor 608 extending to thefirst ring conductor 503. As in the tip conductor 606, the ringconductor 608 may be a continuous conductor or may be a plurality ofconductors that are electrically interconnected. A capacitor 610 iselectrically coupled between the tip conductor 606 and the second ringelectrode 604. The capacitor 610 may take the form of a singlecapacitive device, a plurality of capacitive devices that areelectrically interconnected, or one or more capacitive deviceselectrically interconnected with other electronic devices.

[0029] It is often advantageous for patents suffering from certainconditions to be examined using MRI processes or to be therapeuticallytreated using diathermy processes. However, patients having implantablemedical devices within their bodies have typically been discouraged fromundergoing such processes, as described above. The present invention, asillustrated in FIGS. 2-6, seeks to reduce this detrimental effect bydissipating induced current in the tip conductor 304, 404, 606 intotissue adjacent the ring electrode 302, 402, 604, as well as into tissueadjacent the tip electrode 202, 502. In this way, the heat, produced bythe dissipating currents, is dispersed over a larger portion of tissue,thus decreasing the likelihood of damage to the tissue.

[0030] It is desirable, however, for pacing, stimulation, or sensedsignals (e.g., signals of an electrogram or the like) being transmittedover the tip conductor 304, 404, 606, from or to the tip electrode 202,502, not to be transmitted through the ring electrode 302, 402, 604.Rather, it is desirable for substantially all of such signals to betransmitted between the implantable electronic device 106 and the tipelectrode 202, 502. Accordingly, the capacitors 306, 408, 610 performfiltering functions. A high frequency current such as is induced withinthe lead conductors during MRI or diathermy procedures are routed bothto the ring electrodes 302, 402, 604, respectively, and the tipelectrodes 202, 502. However, substantially all of the low-frequencypacing, stimulation, and/or sensed signals traveling over the tipconductors 304, 404, 606 are routed only to the tip electrodes 202, 502.For the purposes of this disclosure, the phrase “substantially all” ofthe pacing, stimulation, or sensed signals is defined as a level ofsignal at which the implantable medical device 102 is capable ofoperating properly.

[0031] The shunting assembly 208, 504 operates by employing the variableimpedance characteristics of the capacitor 306, 408, 610. Generally,currents induced in conductors (e.g., the tip conductor 304, 404, 606)by energy fields emitted by MRI and diathermy equipment are greater thanabout one megahertz (MHz). Further, signals, such as pacing signals,stimulation signals, sensed signals, and the like, generally havefrequencies of less than about 500 hertz (Hz). According to embodimentsof the present invention, by taking into account the inherent electricalimpedance of tissue of about 500 ohms (Ω), the capacitance of thecapacitor 306, 408, 610 can be determined such that a portion of thecurrent induced in the tip conductor 304, 404, 606 by the MRI ordiathermy equipment is passed through the capacitor 306, 408, 610 to thering electrode 302, 402, 604, while signals, such as pacing signals,stimulation signals, sensing signals, and the like are not passedthrough the capacitor 306, 408, 610, but are rather transmitted over thetip conductor 304, 404, 606 directly to the tip electrode 202, 502. Inother words, the capacitor 306, 408, 610 acts as a filter to only allowcurrents having frequencies within a certain range to be routed to thering electrode 302, 402, 604. In one embodiment, the capacitor 306, 408,610, in combination with the impedance of the tip electrode 202 and thetissue, allows a high-pass filter to be created at certain frequenciessuch as those exceeding 1 MHz.

[0032] For example, given MRI-induced currents having a frequency of twoMHz and a sensed signal (e.g., an electrogram signal, or the like) of100 Hz, a one nanofarad (nF) capacitor (e.g., the capacitor 306, 408,610, or the like) has a electrical impedance of about 80 Ω at afrequency of about two MHz and has a electrical impedance of about 1.6megohms (MΩ) at a frequency of about 100 Hz, as demonstrated by theequation: $X_{c} = \frac{1}{2\pi \quad f\quad c}$

[0033] wherein:

[0034] X_(C) the impedance of the capacitor (Ω);

[0035] f=the frequency (Hz); and

[0036] c=the capacitance of the capacitor (F).

[0037] Thus, in this example, the induced currents would pass throughthe tip electrode 202, 502, as well as through the capacitor 306, 408,610 to the ring electrode 302, 402, 604, since the electrical impedanceof the capacitor 306, 408, 610 is about 160 Ω, which is less than theelectrical impedance of tissue adjacent the tip electrode 202, 502 andthe ring electrode 302, 402, 604 (500 Ω). In this case, the inducedcurrents would be divided approximately 14 percent (80 Ω/580 Ω) to thetip electrode 202, 502 and approximately 86 percent (500 Ω/580 Ω) to thering electrode 302, 402, 604. The sensed signal would be substantiallyunaffected, since the electrical impedance of the capacitor 306, 408,610 is about 1.6 MΩ at 100 Hz, thereby providing a high-pass filteringeffect.

[0038] In one embodiment, the electrical impedance of the capacitor 306,408, 610 at frequencies typical of the induced current is below aboutone-fifth (about 20 percent) of the impedance of the tissue adjacent thetip electrode 202, 502 and adjacent the ring electrode 302, 402, 604(e.g., 100 Ω in the example). In another embodiment, the electricalimpedance of the capacitor 306, 408, 610 at frequencies typical ofpacing, stimulation, or sensed signals is about ten times the impedanceof the tissue adjacent the tip electrode 202, 502 and adjacent the ringelectrode 302, 402, 604 (e.g., 5000 Ω in the example). Further, bysizing the surface area of the ring electrode 302, 402, 604 to be atleast about three times the surface area of the tip electrode 202, 502,the current density may be reduced by at least about four times, thusleading to a commensurate reduction in temperature rise in the tissueadjacent the tip electrode 202, 502 and the ring electrode 302, 402,604. In one embodiment, the surface area of the tip electrode 202, 502,as discussed herein, refers to the surface area of the tip electrode202, 502 omitting any surface area attributed to microstructural pits,crevices, indentations, or the like that may be conventionally used toincrease the electrical contact area of the tip electrode 202, 502. Suchmicrostructural pits, crevices, indentations, or the like, in oneembodiment, may have diameters of less than about 200 micrometers.

[0039] A shunting assembly 702 according to one embodiment of thepresent invention is illustrated in FIG. 7. The shunting assembly 702,which may, in one embodiment, be hermetically sealed, includes a tube704 that is joined (e.g., by welds 706 or the like) to end caps 708,710. Capacitors 712, 714 are electrically connected with and joined(e.g., by welds 716 or the like) to the end caps 708, 710, respectively.In one embodiment, the capacitors 712, 714 are discoidal capacitors orthe like having central contacts 711, 713, respectively, and peripheralcontacts 715, 717, respectively. The shunting assembly 702 furtherincludes pins 718, 720 that are interconnected by a central conductor722 by joints 724. The pins 718, 720 are electrically connected with thecentral contacts 711, 713, respectively. Further, the pin 718 iselectrically connected with a proximal conductor 726 (shown in phantom)of the lead 110, which is electrically connectable with the implantableelectronic device 106. The pin 720 is electrically connected with adistal conductor 728 (shown in phantom) of the lead 110, which iselectrically connected with the tip electrode 202, 502 (FIGS. 2 and 5).Thus, the proximal conductor 726, the pin 718, the central conductor722, the pin 720, and the distal conductor 728 comprise the tipconductor 304, 404, 606 (FIGS. 3, 4, and 6).

[0040] The capacitors 712, 714 are selected as described above, suchthat signals having a certain range or ranges of frequencies (i.e.,induced currents) may flow both through the tip conductor 304, 404, 606to the tip electrode 202, 502 and through the tube 704, which serves asthe ring electrode 302, 402, 604. Signals having another range or rangesof frequencies (i.e., pacing, stimulation, sensed signals, or the like)may substantially only flow through the tip conductor 304, 404, 606 tothe tip electrode 202, 502, as the capacitors 712, 714 have sufficientimpedance to prevent the signals from flowing therethrough. While twocapacitors 712, 714 are illustrated in FIG. 7, the present inventionencompasses a shunting assembly 702 having one or more capacitors suchas the capacitors 712, 714. Thus, the shunting assembly 702 is oneembodiment of the shunting assembly 208, 504 illustrated in FIGS. 2-6.

[0041] A method according to one embodiment of the present invention isillustrated in FIG. 8. In one embodiment, the method includesselectively routing an electrical current traveling through a conductor(e.g., the tip conductor 304, 404, 606 or the like) electrically coupledwith body tissue (e.g., tissue of the patient 104 or the like) over atleast one of a primary path and a secondary path to the body tissuebased upon the characteristic of the electrical current (block 802). Inone embodiment, the primary path may be through the tip conductor 304,404, 606 and the tip electrode 202, 502. Further, the secondary path maybe through the capacitor 306, 408, 610 and the ring electrode 302, 402,604. In one embodiment, the characteristic of the electrical currentcomprises the frequency of the electrical current.

[0042] In another embodiment of the present invention, selectivelyrouting the electrical current, as described above, further comprisesrouting the current over the primary path and the secondary path to thebody tissue if the current is induced in the conductor by a field (block804). In a further embodiment, selectively routing the electricalcurrent, as described above, further comprises routing the current onlyover the primary path to the body tissue if the current is not inducedin the conductor by a field (block 806).

[0043] While the operation of the present invention has been disclosedrelative to energy fields emitted by MRI and diathermy equipment, thepresent invention is not so limited. Rather, the operation of thepresent invention is equally applied to energy fields emitted byequipment other than MRI and diathermy equipment.

[0044] The particular embodiments disclosed above are illustrative only,as the invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

What is claimed is:
 1. An electrical lead, comprising: an elongate body having a proximal end portion and a distal end portion; a first electrode disposed adjacent and joined to the distal end portion of the elongate body; a first conductor extending between the proximal end portion and the distal end portion of the elongate body and being electrically coupled to the first electrode; a second electrode disposed adjacent the first electrode and joined to the elongate body; and a capacitive device electrically coupled to the first conductor and the second electrode.
 2. An electrical lead, according to claim 1, further comprising a second conductor extending between the proximal end portion of the elongate body and the second electrode and being electrically coupled to the second electrode.
 3. An electrical lead, according to claim 1, further comprising: a third electrode disposed adjacent the second electrode and joined to the elongate body; and a second conductor extending between the proximal end portion of the elongate body and the third electrode and being electrically coupled to the third electrode.
 4. An electrical lead, according to claim 1, wherein: the capacitive device further comprises a discoidal capacitor having a central contact and a peripheral contact; the first conductor is electrically coupled with the central contact; and the second electrode is electrically coupled with the peripheral contact.
 5. An electrical lead, according to claim 1, wherein: the first electrode and the second electrode are capable of being electrically coupled with body tissue; the first conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance substantially less than electrical impedance of the body tissue at signal frequencies greater than those used to sense biological signals or deliver electrical stimulation to the body tissue.
 6. An electrical lead, according to claim 1, wherein: the first electrode and the second electrode are capable of being electrically coupled with body tissue; the first conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance substantially greater than an electrical impedance of the body tissue at signal frequencies used to sense biological signals or deliver electrical stimulation to the body tissue.
 7. An electrical lead, according to claim 1, wherein an area of the second electrode is at least three times an area of the first electrode.
 8. An electrical lead, according to claim 1, wherein the capacitive device is capable of allowing at least a portion of a current, induced in the first conductor by a field, to be routed to the second electrode.
 9. A shunting assembly, comprising: an electrode; a conductor; and a capacitive device electrically coupled with the electrode and the conductor.
 10. A shunting assembly, according to claim 9, wherein: the capacitive device further comprises a discoidal capacitor having a central contact and a peripheral contact; the conductor is electrically coupled with the central contact; and the electrode is electrically coupled with the peripheral contact.
 11. A shunting assembly, according to claim 9, wherein: the capacitive device further comprises a first discoidal capacitor having a central contact and a peripheral contact and a second discoidal capacitor having a central contact and a peripheral contact; the conductor further comprises a first pin and a second pin electrically coupled by a central conductor; the first pin is electrically coupled with the central contact of the first discoidal capacitor; the second pin is electrically coupled with the central contact of the second discoidal capacitor; and the electrode is electrically coupled with the peripheral contact of the first discoidal capacitor and the peripheral contact of the second discoidal capacitor.
 12. A shunting assembly, according to claim 9, wherein: the electrode is capable of being electrically coupled with body tissue; the conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance of less than an electrical impedance of the body tissue when the electrical current is induced during MRI or diathermy therapies.
 13. A shunting assembly, according to claim 9, wherein: the electrode is capable of being electrically coupled with body tissue; the conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance of greater than an electrical impedance of the body tissue when transferring a signal having at frequencies of the electrical current less than or equal to 500 hertz.
 14. A shunting assembly, according to claim 9, wherein the electrode further comprises a tube having a first end and a second end, wherein the shunting assembly further comprises: a first end cap joined to the first end of the tube; and a second end cap joined to the second end of the tube.
 15. A shunting assembly, according to claim 9, wherein the shunting assembly is hermetically sealed.
 16. A shunting assembly, according to claim 15, wherein the capacitive device is capable of allowing at least a portion of a current, induced in the first conductor by a field, to be routed to the second electrode.
 17. A medical device, comprising: a control unit; an elongate body having a proximal end portion coupled with the control unit and a distal end portion; a first electrode disposed adjacent and joined to the distal end portion of the elongate body; a first conductor extending between the proximal end portion and the distal end portion of the elongate body and being electrically coupled to the first electrode and the control unit; a second electrode disposed adjacent the first electrode and joined to the elongate body; and a capacitive device electrically coupled to the first conductor and the second electrode.
 18. A medical device, according to claim 17, further comprising a second conductor extending between the proximal end portion of the elongate body and the second electrode and being electrically coupled to the second electrode and the control unit.
 19. A medical device, according to claim 17, further comprising: a third electrode disposed adjacent the second electrode and joined to the elongate body; and a second conductor extending between the proximal end portion of the elongate body and the third electrode and being electrically coupled to the third electrode and the control unit.
 20. A medical device, according to claim 17, wherein: the capacitive device further comprises a discoidal capacitor having a central contact and a peripheral contact; the first conductor is electrically coupled with the central contact; and the second electrode is electrically coupled with the peripheral contact.
 21. A medical device, according to claim 17, wherein: the first electrode and the second electrode are capable of being electrically coupled with body tissue; the first conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance of no more than about 20 percent of an electrical impedance of the body tissue at a frequency of the electrical current greater than about 1 Mhz.
 22. A medical device, according to claim 17, wherein: the first electrode and the second electrode are capable of being electrically coupled with body tissue; the first conductor is capable of transmitting an electrical current; and the capacitive device has an electrical impedance about ten times of an electrical impedance of the body tissue at a frequency of the electrical current less than 500 hertz..
 23. A medical device, according to claim 17, wherein an area of the second electrode is at least three times an area of the first electrode.
 24. A medical device, according to claim 17, wherein the capacitive device is capable of allowing at least a portion of a current, induced in the first conductor by a field, to be routed to the second electrode.
 25. A medical device, according to claim 17, wherein the capacitive device is capable of preventing at least most of a signal transmitted over the first conductor from the control unit from being routed to the second electrode.
 26. A medical device, according to claim 17, wherein the capacitive device is capable of preventing at least most of a signal transmitted over the first conductor to the control unit from being routed to the second electrode.
 27. A method, comprising selectively routing an electrical current traveling through a conductor electrically coupled with body tissue over at least one of a primary path and a secondary path to the body tissue based upon a characteristic of the electrical current.
 28. A method, according to claim 27, wherein selectively routing the electrical current traveling through the conductor further comprises selectively routing the electrical current traveling through the conductor over at least one of the primary path and the secondary path to the body tissue based upon the frequency of the electrical current.
 29. A method, according to claim 27, wherein selectively routing the electrical current traveling through the conductor further comprises: routing the current over the primary path and the secondary path to the body tissue if the current is induced in the conductor by a field; and routing the current only over the primary path to the body tissue if the current is not induced in the conductor by the field.
 30. An apparatus, comprising means for selectively routing an electrical current traveling through a conductor electrically coupled with body tissue over at least one of a primary path and a secondary path to the body tissue based upon a characteristic of the electrical current.
 31. An apparatus, according to claim 30, wherein the means for selectively routing the electrical current traveling through the conductor further comprises means for selectively routing the electrical current traveling through the conductor over at least one of the primary path and the secondary path to the body tissue based upon the frequency of the electrical current.
 32. An apparatus, according to claim 30, wherein the means for selectively routing the electrical current traveling through the conductor further comprises: means for routing the current over the primary path and the secondary path to the body tissue if the current is induced in the conductor by a field; and means for routing the current only over the primary path to the body tissue if the current is not induced in the conductor by the field. 